U.S. patent number 5,714,213 [Application Number 08/226,379] was granted by the patent office on 1998-02-03 for securtiy element.
This patent grant is currently assigned to Landis & Gyr Betriebs AG. Invention is credited to Gregor Antes, Walter Trachslin.
United States Patent |
5,714,213 |
Antes , et al. |
February 3, 1998 |
Securtiy element
Abstract
A security element for the authentication of a substrate has a
pattern comprising optical diffraction elements which are embossed
in a carrier material of plastic material and unembossed neutral
areas. On the embossing side of the carrier material a reflecting
layer covers only surfaces with relief structures of the
diffraction elements while the neutral areas which lie between are
free of the reflecting layer and are therefore non-reflecting. If
the security element is stuck in the form of a stamp onto the
substrate and the carrier material is transparent, image portions,
which are covered by the stamp, of a feature on the substrate can
be discerned through the neutral areas.
Inventors: |
Antes; Gregor (Zurich,
CH), Trachslin; Walter (Walchwil, CH) |
Assignee: |
Landis & Gyr Betriebs AG
(Zug, CH)
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Family
ID: |
4246515 |
Appl.
No.: |
08/226,379 |
Filed: |
April 12, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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933986 |
Aug 21, 1992 |
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Foreign Application Priority Data
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Oct 14, 1991 [CH] |
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03 006/91-8 |
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Current U.S.
Class: |
428/30; 101/28;
283/72; 283/91; 428/142; 428/187; 428/908; 428/458; 428/913;
428/916 |
Current CPC
Class: |
B42D
25/328 (20141001); B42D 25/47 (20141001); B42D
25/351 (20141001); B42D 25/425 (20141001); B42D
25/324 (20141001); Y10T 428/31681 (20150401); Y10S
428/913 (20130101); Y10S 428/916 (20130101); Y10S
428/908 (20130101); Y10T 428/24364 (20150115); Y10T
428/24736 (20150115) |
Current International
Class: |
B42D
15/10 (20060101); B24D 015/00 (); B44F 001/10 ();
B32B 001/00 () |
Field of
Search: |
;283/86,72,77,91,94,108,109,92
;428/30,29,67,142,156,13,458,908,916,913,187 ;264/1.3,1.7,1.9,293
;101/28,29 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0170832 |
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Feb 1986 |
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EP |
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0439092 |
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Jul 1991 |
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EP |
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Primary Examiner: Thibodeau; Paul J.
Assistant Examiner: Sand; Stephen
Attorney, Agent or Firm: Meltzer, Lippe, Goldstein, Wolf
& Schlissel, P.C.
Parent Case Text
This is a continuation of application Ser. No. 07/933,986, filed
Aug. 21, 1992 now abandoned.
Claims
What is claimed is:
1. A security element comprising a carrier made of transparent
plastics material and a reflective layer, the carrier having one
surface as an embossing side, at least one portion of said
embossing side being embossed with a pattern of linear diffraction
elements with microscopic relief structures separated by unembossed
neutral areas, said reflective layer covering only said embossed
linear diffraction elements and leaving said unembossed neutral
areas uncovered and transparent, said linear diffraction elements
being optically diffractive and said unembossed neutral areas being
non-diffractive and non-reflective, and said embossed linear
diffraction elements and unembossed non-reflective neutral areas
forming a visible pattern, wherein said visible pattern does not
obstruct transparency of said security element in the neutral
areas.
2. A security element as forth in claim 1, further comprising a
protective layer covering the entire embossing side of said
carrier, said reflective layer being located between said carrier
and said protective layer, said protective layer being of the same
material as said carrier.
3. A security element as set forth in claim 1, further comprising a
stabilization layer, wherein said stabilization layer and the
surface opposite to the embossing side of said carrier are
connected by a lacquer layer to form a covering material with said
linear diffraction elements embossed into the embossing side of
said carrier, said covering material being transparent so that said
pattern can be viewed through said covering material.
4. A security element as set forth in claim 1, further comprising a
stabilization layer, wherein said stabilization layer and the
surface opposite to the embossing side of said carrier are
connected by a lacquer layer to form a covering material with said
linear diffraction elements embossed into the embossing side of
said carrier, and said covering material being transparent so that
said pattern can be viewed through said coveting material, wherein
said security element further comprises a protective layer covering
the entire surface on the embossing side of said carrier, said
reflective layer being located between said carrier and said
protective layer.
5. A security element as set forth in claim 3, wherein said carrier
on the embossing side is covered by an adhesive layer to adhere the
security element to a substrate having an identification feature
thereon, and said covering material and said adhesive are
transparent, so that transparency of the security element and
discernibility of of the identification feature beneath said
security element are not obstructed in the neutral areas.
6. A security element as set forth in claim 2, wherein said
protective layer is covered by an adhesive layer to adhere the
security element to a substrate with an identification feature
thereon, and said covering material and said protective and
adhesive layers are transparent, so that transparency of the
security element and discernibility of the identification feature
beneath said security element are not obstructed in the neutral
areas.
7. A security element as set forth in claim 1, wherein said linear
diffraction elements are lines or dots having a width of less than
0.5 mm and are spaced apart by said unembossed neutral areas and
form said pattern.
8. A security element as set forth in claim 1 or 3, wherein said
carrier is adapted to be glued onto a substrate having an
identification feature thereon by an adhesive layer being applied
on the embossing side of said carrier and covering the entire
substrate having an identification feature thereon completely, so
that said reflective layer covering the linear diffraction elements
is enclosed between the adhesive and the carrier, and said layers
over the substrate are transparent so that discernability of the
identification feature beneath the security element is not
obstructed in said neutral areas.
9. A security element as set forth in claim 1, wherein the sum of
the surface areas of said neutral areas which are between said
diffraction linear elements is greater than the sum of the surface
areas of said diffraction elements.
10. A security element as set forth in claim 1, wherein said
microscopic relief structure is comprised of depressions which
extend to a depth into said carrier layer of at least one
micrometer beneath the level of said unembossed neutral areas.
11. A security element as set forth in claim 10, wherein said
depressions are filled with a transparent protective lacquer having
an index of refraction different from that of the covering
material, so that the interface between the covering material and
the protective lacquer acts as said reflective layer due to a
change in index of refraction.
12. An embossing die for embossing the security element as set
forth in claim 1, said die having raised embossing structures for
producing a mesa structure with depressions in said carrier at the
areas to be reflective, said raised embossing structure having flat
tops with said microscopic relief structures, wherein the raised
embossing structures reproduce said microscopic relief structures
at the floor of the depressions, said embossing structures
corresponding to said linear diffraction elements of said security
element, said microscopic relief structures on top of said raised
embossing structures of said die being raised above a plane defined
for said neutral areas of said security elements.
13. A security element as set forth in claim 2, 4 or 11 wherein
said protective layer is cured with radiation.
14. The security element of claim 4 wherein said protective layer
is the same material as said carrier.
15. A security element as set forth in claim 4, wherein said
protective layer is covered by an adhesive layer to adhere the
security element to a substrate with an identification feature
thereon, and said covering material and said protective and
adhesive layers are transparent, so that transparency of the
security element and discernibility of the identification feature
beneath said security clement are not obstructed in the neutral
area.
16. A security element comprising a carrier of light absorbent
plastics material and a reflective layer, the carrier having one
surface as an embossing side, at least one portion of said
embossing side being embossed with a pattern of linear diffraction
elements with microscopic relief structures separated by unembossed
neutral areas, said reflective layer covering only said embossed
linear diffraction elements and leaving said unembossed neutral
areas uncovered and absorbent, said linear diffraction elements
being optically diffractive and said non-embossed neutral areas
being non-diffractive and non-reflective, and said embossed linear
diffraction elements and unembossed non-reflective neutral areas
forming a visible pattern covered by a transparent protective
layer.
Description
FIELD OF THE INVENTION
The invention relates to a security element. Such security elements
are suitable for example for safeguarding a photograph which is
stuck on a personal identity card, wherein the security element
which is in the form of a stamp covers over both a part of the
surface of the photograph and also a part of the surface of the
identity card The invention also relates to a process for the
production of such a security element.
DESCRIPTION OF THE PRIOR ART
European patent application EP-A-401 466 describes such a security
element which has a reflection layer over its entire surface and
shows a pattern which is composed of surfaces with embossed relief
structures and unembossed surfaces arranged therebetween. When the
security element is visually viewed, the reflection phenomena of
high light intensity at the unembossed surfaces interfere with the
full colour development of the light which is diffracted at the
relief structures.
European patent EP 169 329 describes an apparatus for the
production of dies with which the microscopic relief structures are
embossed for example into plastic carries which are aluminised on
one side. The improved apparatus disclosed in European patent
application EP-A-330 738 permits the production of the dies which
are required for embossing of the relief structures and which have
surface portions with at least a dimension of less that 0.3 mm.
European patent application EP-A-253 089 discloses interrupting the
reflection layer in the region of the relief structures in a
predetermined pattern in order to achieve good adhesion between a
carrier for the relief structures and a protective layer covering
the latter.
European patent application EP-A-439 092 describes the use of the
security element, with diffraction structures which are covered
with the reflection layer in surface portions in a grid-like
configuration for safeguarding identity certificates, wherein the
features of the identity certificate which are covered by the
security element can be discerned through non-reflecting surface
portions in spite of a clouding effect due to the grid
configuration.
OBJECT AND SUMMARY OF THE PRESENT INVENTION
The object of the invention is that of providing a security element
having a pattern comprising relief structures with an
optical-diffraction element and unembossed neutral areas, in which
visual observation of the pattern is not disturbed by the light
which is reflected at the neutral areas, and providing an
inexpensive production process therefor.
In accordance with one aspect of the present invention, there
provided a security element comprising a carrier layer of plastics
material and a reflective layer, the carrier layer having a
surface, least one portion of said surface being embossed with
microscopic relief structures so that said embossed portion of said
surface optically diffractive, at least one other portion of said
surface being an unembossed neutral portion so that said embossed
portion and said unembossed portion from a visible pattern, and
said reflective layer coveting only said microscopic relief
structures so that said unembossed portion is not reflective.
In accordance with another aspect of the present invention, there
is provided a process tot producing a security element, comprising
steps of: embossing a surface of a plastics carrier layer through
reflective layer cart led by said surface of said carrier layer so
as to produce optically diffractive microscopic relief structures
in at lest one portion of said surface and so as to leave at least
one portion of said surface as an unembossed neutral portion;
covering only microscopic relief structures with a protective
lacquer so that said neutral portion remains substantially free of
said protective lacquer; removing said reflective layer from said
carrier layer to expose said unembossed neutral portion; and
applying a protective layer over the reflective layer in said
embossed portion and the carrier Layer in the unembossed
portion.
In accordance with a further aspect of the present invention, there
is provided a process for producing a security element, comprising
the steps of: embossing a surface of a plastics carrier layer using
an embossing die having raised embossing relief structures to
produce embossed optically diffractive microscopic relief
structures in at least one portion of said surface of said carrier
layer and so as to leave al least one portion of said surface as an
unembossed neutral portion; covering said unembossed neutral
portion with a separating layer of material which can be washed off
or otherwise chemically removed; covering said microscopic relief
structures in said embossed portion and said separating layer in
said unembossed portion with a reflecting layer; removing said
separating layer together with said reflecting layer in said
unembossed portion; and applying a protective layer over said
carrier layer cover said carrier layer in said unembossed portion
and said reflective layer in said embossed portion.
Other objects, features and advantages of the present invention
will become apparent upon consideration of the following detailed
description of a preferred embodiment thereof, especially when
considered with the accompanying drawings in which like reference
numerals are employed to designate the same or similar components
the different figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows an identity card or pass with d security element,
FIG. 2 shows a stamp in cross-section,
FIG. 3a through 3d shows the operation of covering relief
structures with a protective lacquer by means of a printing
FIG. 4a through 4c show the operation of covering the relief
structures with the protective lacquer by an intaglio printing
process,
FIG. 5a through 5d show the operation of covering the structures
with a protective lacquer by a relief printing process,
FIG. 6 shows the stamps on a carrier strip,
FIG. 7a and 7b show the production of an embossing tile, and
FIG. 8 shows the embossing die with raised diffraction
elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1, reference numeral 1 identifies a substrate comprising
paper, plastic material, metal and the like, on the surface of
which is disposed a feature 2. A stamp 3 of plastic material, as a
security element, covers over adjacent surface portions of the
substrate 1 and the feature 2, wherein the stamp 3 is stuck with
one surface portion onto the feature 2 and with the other surface
portion onto the substrate 1. The substrate 1 can be an identity
card or pass, in which case the feature 2 can be a photograph of
the owner, a signature which is written before the stamp 3 is
applied, or another distinguishing mark.
The stamp 3 has a pattern which is composed of surfaces with an
optical-diffraction effect, with diffraction elements 4, and
neutral areas 5. The diffraction elements 4 diffract the incident
ambient light in a reflection mode and produce a characteristic
colour image which alters when the substrate 1 is tilted. The
neutral areas 5 do not reflect; they are for example absorbent or
transparent. If the neutral areas 5 are transparent, only a low
degree of reflection can be observed in the areas 5 at the surface
of the stamp 3, because of the sudden change in the indices of
refraction of the media (air-plastic material), without however
that disturbing either the colour image or observation of the
substrate 1 or feature 2 which is visible at that location, through
the stamp 3.
The security element has a particularly advantageous effect in a
visual observation situation if the diffraction elements 4 are for
example of linear configuration and form filigree patterns on the
security element. Those patterns have the advantage that the
feature 2 which is under the stamp 3 can be easily discerned, in
particular if the lines of the diffraction elements 4 are as narrow
as possible. The line widths can be smaller than 0.5 mm, for
example 0.1 mm, 0.05 mm or even narrower. It is also possible to
use a dot grid or a pattern which is made up of dots, in which case
the diameter of the diffraction elements 4 which are in the form of
dots approximately corresponds to the above-indicated line widths.
Line widths of from about 25 .mu.m can be achieved with the means
which are described in EP-A-330 738 (corresponding to U.S. Pat. No.
4,984,824) bearing the title "Document" by Antes et al, and the
text of which is expressly incorporated into this description. At
any dot or line portion, it is possible to produce an individual
diffraction element which differs in terms of its parameters,
spatial frequency and grid profile from the adjacent dots or line
portions. The change in the parameters from one diffraction element
4 to the other can serve as for example means of graphic
configuration for enhancing the level of security.
For discernibility of a non-forged feature 2, it is advantageous
for the pattern on the security element to be so designed that the
sum of the surface areas of the neutral areas 5 which are between
the diffraction elements 4 is greater than the sum of the surface
areas of the diffraction elements 4.
The security element has the advantage that, due to reflection of
the diffracted light, the diffraction elements 4 contrast in a
highly conspicuous fashion from the neutral areas 5 having a low
level light intensity and at which there is no reflection and
diffraction of which can mix with the play of colours of the
diffracted light and reduce the brilliance of the diffraction
elements 4. As the image portions 6 of the feature 2 which are
beneath the neutral areas 5 can be discerned through the neutral
areas 5 and those with the image portions 7 which are not covered
by the stamp 3 must provide a complete image in respect of the
feature 2, the stuck-on stamp 3 is also suitable as a security
element for authentication of the feature 2, not only being
distinguished by the high level of visibility of the diffraction
elements 4 and the transparency in the neutral areas 5 but also
affording a visual checkable high level of security against
forgeries in regard to authentication of the feature 2.
If the substrate 1 comprises plastic material, as for example in
the case of a credit card, a brilliant optical-diffraction
identification characteristic 8 with such a pattern, as a security
element, can also be produced directly in the surface of the
substrate 1, without proceeding indirectly via a stuck-on stamp
3.
FIG. 2 is a view in cross-section through the identity card with
the stamp 3 which is stuck on the substrate 1, as the security
element. Shown by way of example is a composite layer configuration
which is described in European patent application EP-A-401 466
(corresponding to U.S. Pat. No. 5,104,471) under the title
"Composite layer configuration with diffraction structures" to the
same applicant, the text of which is expressly incorporated into
the present description.
Enclosed between the substrate 1 and a stabilization layer 9 of
polyester is a carrier 10 of plastic material for the diffraction
elements 4. A lacquer layer 11 provides good adhesion between the
stabilization layer 9 and the carrier 10. The diffraction elements
4 are embossed into the carrier 10, in the form of microscopically
fine relief structures 12. A protective layer 13 provides cover
over the full surface both for the relief structures 12 which are
covered with a reflective layer 14 and also the unembossed and
non-reflecting neutral areas 5 of the carrier 10. An adhesion layer
15 which is applied to the protective layer 13 fixedly joins the
stamp 3 (see FIG. 1) to the substrate 1, in which respect the
adhesive join can be released without any disturbance to the
security element.
Advantageously, the carrier 10 and the protective layer 13 comprise
the same material so that the carrier 10 and the protective layer
13 can be particularly intimately joined in the neutral areas 5, so
that no weak point is formed at the join and the protective layer
13 can be removed for forming the relief structures 12, without
destroying same. If the carrier 10 and the protective layer 13 are
of the same clear material, an undisturbed carrier surface 16 which
is present in the unembossed neutral areas 5 is invisible. The
carrier surface 16 is therefore shown in broken line in the
drawing. The neutral areas 5 therefore remain completely clearly
transparent and do not disturb discernibility of the feature 2
which is under the stamp 3 (FIG. 1). It will be noted however that
the carrier 10 and the protective layer 13 may also be differently
coloured. Instead of the composite layer material, it is also
possible to use a solid foil, for example consisting of PVC, as a
carrier material 17.
If the stamp 3 is to be used for sticking onto the substrate 1,
transparent or completely colourless materials are advantageously
used for the protective layer 13, the adhesive layer 15 and the
carrier material 17 so that the feature 2 (see FIG. 1) remains
visible through the neutral areas 5.
In another configuration, the carrier 10 itself is sufficiently
stable so that the stabilization layer 9 and the lacquer layer 11
are unnecessary.
Production of the security feature is distinguished by a small
number of characteristic steps in the process, which can be seen
from the production processes set forth as examples. For example,
in comparison with the state of the art (EP-A-401 466), only a
small number of additional steps have to be included in the
processes described hereinafter, but, as described below, those
steps are of different natures. Each of those processes has its
advantages.
By way of example, FIGS. 3a through 3d, FIGS. 4a through 4c and
FIGS. 5a through 5d show in sections the stepwise production of a
preliminary material in strip form for stamps 3 (see FIG. 1) with
the security element. To show the successive steps in the
processes, those drawings are turned through 180.degree. relative
to FIG. 2. The strip form makes it possible to use a continuous
process and is therefore suitable for inexpensive mass
production.
In FIG. 3a the carrier material 17 in strip form comprises for
example the stabilization layer 9 and the carrier 10 which are
joined to the lacquer layer 11 (see FIG. 2). The carrier material
17 is covered with a reflecting layer 14 over its full area on the
side remote from the stabilization layer 9, the embossing side. For
example, aluminium layers which are applied by vapour deposition
and the thickness of which is only fractions of a micrometer are
known as the reflecting layer 14.
The carrier material 17 is withdrawn in the form of a strip from a
supply roll (not shown) and passes successively into the different
processing regions in which the stamps 3 (see FIG. 1) with the
security feature are produced step by step.
Process 1
In the first step (FIG. 3a), using for example heated embossing
dies, the microscopic relief structure 12 in the pattern of the
security element is embossed into an embossing side 18 of the
carrier material 17, the side 18 being characterized by the
reflecting layer 14. A respective one of the unembossed neutral
areas 5 is enclosed between each two diffraction elements 4 and
4
In the second step (FIG. 3b), a protective lacquer 19 is applied by
means of a printing process to the embossed diffraction elements 4
in aligned relationship in the register of the patterns of the
diffraction elements 4 (="in accurate register relationship"),
which protective layer accurately covers the reflecting layer 14 on
the surfaces of the diffraction elements 4 and leaves the layer 14
free and exposed on the neutral areas 5. The protective lacquer 19
is for example clearly transparent or coloured and only transparent
in relation to light from a predetermined range of the
spectrum.
The strip of carrier material 17 is then drawn through a chemical
bath. In the bath, the exposed reflecting layer 14 on the neutral
areas 5 is removed. If the reflecting layer 14 comprises aluminium,
a suitable chemical bath is for example dilute caustic soda
solution.
After the washing and drying operations, the carrier material 17
has the structure shown in FIG. 3c. The reflecting layer 14 applied
to the embossed relief structures 12 is only present and covered
with the protective lacquer 19, in the region of the diffraction
elements 4, 4'. The unembossed neutral areas 5 which are between
the diffraction elements 4, 4' are no longer covered with the
reflecting layer 14, the unembossed carrier surface 16 of the
carrier material 17 being exposed.
In the last working operation, the preliminary material for stamps,
which is shown in FIG. 3d, is finished, in which operation the
protective layer 13 is firstly applied to the carrier material 17
on the embossing side 18 (FIG. 3a), over the entire surface area
involved, and lastly the adhesive layer 15 is applied.
The adhesive layer 15 may also be omitted if, immediately prior to
the operation of sticking the stamp 3 (FIG. 1) onto the substrate 1
(FIG. 1), the adhesive is applied to one of the two adhering
components 1, 3 or the protective layer 13 is in the form of an
adhesive layer 15.
That process has the advantage that the embossing dies used for
production of optical-diffraction patterns in accordance with the
state of the art can also be used to produce the novel security
elements so that new embossing dies do not have to be produced.
Process 2
The carrier material 17 which is embossed through the reflecting
layer 14 in FIG. 4a has been embossed by means of an embossing die
described hereinafter, with raised embossing structures. As a
result, the relief structures 12 which are embossed into the
carrier 10 (see FIG. 2) are lowered by a predetermined distance A
into the carrier material 17, that is to say, beneath the carrier
surface 16, with depressions 21 being produced. The distance A is
measured between the surface of the carrier material 17 and the
tips 20, which are closest thereto, of the relief structure 12.
For example, that distance A is between about 1 .mu.m and 5 .mu.m,
while the relief structure 12 has differences in height as
indicated at B of 1 .mu.m or less. The relief structures 12 are
embossed on the floor of the depressions 21 and may therefore also
involve differences in height as indicated at B of more than 1
.mu.m. As a result, the carrier material 17 in FIG. 4a has a mesa
structure, with the unembossed areas 5 representing the plateau and
the depressions 21 with the relief structures 12 representing the
dips or valleys.
Application of the protective lacquer 19, as shown in FIG. 4b, is
effected when the carrier material 17 passes through an applicator
mechanism 22, 23 which is known in the printing art for intaglio
printing. The carrier material 17 moves in a transportation
direction 24 from the roller support frame 22 to the scraper blade
23 comprising for example plastic or rubber material. The scraper
blade 23 is arranged above the carrier material 17, and the edge of
the scraper blade 23 can slide in lightly resilient contact against
the reflecting layer 14 over the entire width of the carrier
material 17 for removal of the excessive protective lacquer 19.
The protective lacquer 19 is uniformly distributed over the
reflecting layer 14 as the carrier material 17 passes through the
arrangement. By virtue of selection of the appropriate properties
for the protective lacquer 19 such as viscosity, wetting etc., the
numerical values of which are ascertained by testing, the
protective lacquer 19 also fills in particular the depressions 21
and covers over the relief structures 12. The scraper blade 23
scrapes the protective lacquer 19 which is on the unembossed
neutral areas 5 off the reflecting layer 14 so that the protective
lacquer 19 then only remains in the depressions 21 and protects the
reflecting layer 14 of the diffraction elements 4 from the effect
of the chemical bath for removal of the reflecting layer 14.
Subsequently to the operation of drying the protective lacquer 19,
the strip of carrier material 17 is drawn through the chemical bath
and the exposed reflecting layer 14 is removed in the areas 5, as
in process 1. FIG. 4c shows the preliminary material which is in
the finished state, by way of example, in which the reflecting
layer 14 has remained only on the diffraction elements 4. Only the
protective layer 13 is present on the carrier material 17, over the
entire surface area.
That process has the advantage that there is no need for operating
in accurate register relationship when applying the protective
lacquer 19 as that occurs automatically and with a high level of
precision. It is even possible for the embossing operation and the
step of applying the protective layer 13 and the protective lacquer
19 to be carried out at different production locations without that
adversely affecting the accuracy with which the reflecting layers
14 are restricted to the diffraction elements 4.
The arrangement of the relief structures 12 on the floor of the
depressions 21 in the carrier material 17 is advantageous as that
provides maximum protection for the relief structures 12 (FIG. 4b)
when the diffraction elements 4 are being covered with the
protective lacquer 19. For the sake of completeness it should also
be mentioned that application of the protective lacquer 19, in
accordance with process 1, can also be carried out on the carrier
material 17 with the mesa structure.
Process 3
Production of the security elements can also be carried out with a
starting material as the carrier material 17 which, as shown in
FIG. 5a, does not have a reflecting layer 14 (FIG. 3a) on the
embossing side 18. As in process 2, the diffraction elements 4 and
the depressions 21 in the carrier material 17 are produced by means
of the embossing die with raised embossing structures.
After the operation of embossing the carrier material 17, a
printing mechanism which is known from relief printing and which is
illustrated here only by means of its applicator roller 26 is used
to apply in accurate register relationship to the surfaces of the
unembossed neutral areas 5 in FIG. 5b a material which can be
washed off, as a separating layer 25, in accordance with EP-A-253
089. The roller 26 rolls against the embossing side 18 of the
carrier material 17 and covers the raised neutral areas 5 with the
separating layer 25. The viscosity and thickness of application of
the material which can be washed off are so selected that that
material does not fill the depressions 21 and contaminate the
relief structures 12 (see FIG. 2). Therefore the separation layer
25 only covers over the neutral regions 5 and the relief structures
12 which are embossed in the depressions 21 remain free.
As can be seen from FIG. 5c, the carrier material 17 which is
partially covered with the separating layer 25 is then coated with
the reflecting layer 14, both on the relief structures 12 in the
depressions 21 and also on the separating layer 25.
After a washing operation which removes the wash-off material of
the separating layer 25 together with the reflecting layer 14
directly applied thereto, in FIG. 5d the preliminary material then
only still has the reflecting layer 14 in the diffraction elements
4 while the carrier material 17 is exposed in the neutral areas 5.
Finally, the full surface of the carrier material 17 is covered
with the protective layer 13, the depressions 21 being filled with
the material of the protective layer 13.
The advantage of this process is a shorter passage time through the
apparatus in production of the preliminary material as the step in
the process for applying the protective lacquer 19 (FIG. 4c) is
omitted.
It is also possible to have a combination of individual steps from
the three processes. In particular, starting from an embossed
carrier material 17 as shown in FIG. 5a, without reflecting layer
14 (see FIG. 4b), the protective lacquer 19 can be applied by means
of the printing process as in FIG. 3b or with the process
illustrated in FIG. 4b. The carrier material 17 and the protective
lacquer 19 in FIG. 4c advantageously differ from each other in
regard to their index of refraction. In its index of refraction,
the carrier material 17 is of a value of lower than 1.5 while the
protective lacquer 19 over the diffraction elements 4 has an index
of refraction of over 1.55. The jump in index of refraction at the
interface between the carrier material 17 and the protective
lacquer 19 causes strong reflection of the light which is incident
on the diffraction elements 4 through the carrier material 17 so
that that interface forms the reflecting layer 14 and produces the
same effect. The absence of the metallic reflecting layer 14
additionally produces a strong unreleasable join between the layers
at the diffraction elements 4.
A protective lacquer 19 which can be hardened by means of
irradiation has the advantage that, when the protective lacquer 19
is hardened, in the depressions 21 (see FIG. 5a), a highly robust
support which is stable in relation to heat is formed, for the
accurately shaped relief structures 12 (see FIG. 2) in the
diffraction elements 4. The stamps 3 which are made from such a
material (FIG. 1), even without a stabilization layer 9 (see FIG.
2), withstand the effect of the heat which is required when the
stamps 3 are applied by a hot adhesive operation or by
over-lamination.
Advantageously, the carrier material 17 is transparent and at least
the protective lacquer 19 (FIG. 3b) or the protective layer 13 is
coloured dark or completely black as the viewer can discern the
identification characteristic 8 as a conspicuously brilliant
filigree-like pattern, for example in the form of fine lines in
front of a dark background. If the reflecting layer 14 is not
applied in accurate register relationship, reflecting
non-diffracting surfaces which can be easily discerned by the naked
eye occur beside the linear diffraction structures 4.
The security element can be used for ascertaining the authenticity
of documents, banknotes and other items. The pattern of the
security element and the features 2 which are beneath the stamp 3,
such as graphic or script elements which are printed on the
substrate or a watermark in the substrate are also discernible with
the naked eye by a layman if, except for the reflecting layer 14,
the protective layer 13 and the carrier material 17 are
transparent. A quasi-transparent security element of that kind has
a fine filigree-like pattern comprising the diffraction elements 4
can exhibit a brilliant play of colours depending on the incidence
of light and the direction of observation, without discernibility
of the graphic or script elements through the clear neutral areas 5
suffering as a result.
The quasi-transparent security element can advantageously be used
for partially or totally covering the substrate 1 which is to be
safeguarded against forgery, and the features 2 thereof. Personal
identity cards with printing thereon and a photograph of the owner
have been mentioned by way of example of such substrates 1. The
graphic pattern of the stamp 3 covers over the features 2 with the
fine lines or line elements whose relief structure 12 act as
diffraction elements 4. Because of the high level of
light-diffracting efficiency of the diffraction elements 4, a small
surface proportion of the diffraction elements 4 is sufficient so
that discernment of the items of information on the substrate 1
through the neutral areas 5 is not adversely affected.
The linear diffraction elements 4 advantageously have profile
shapes and spatial frequencies which vary in a predetermined
fashion along the 1 lines so that the visual impress ion changes in
a predetermined fashion along the lines if the conditions of
viewing are altered, for example due to the substrate 1 being
turned or tilted. An attempt at changing the features 2 which are
under the security element destroys the security element. Forgery
of the pass or identity card, for example by fitting together
pieces of a number of genuine passes or identity cards, can be
easily detected as the fine lines of the diffraction elements are
displaced at joins or continue in a broken configuration. By a
tilting movement, the substrate can be easily checked by means of
the striking diffraction effects, even by lay people, to ascertain
whether the fine diffraction elements 4 which cover the items of
information are intact, for example by checking whether the
diffraction effects of the diffraction elements 4 do or do not
change abruptly along the fine lines.
If the carrier material 17 is sufficiently stiff, the cards can be
stamped in the credit card format directly out of the preliminary
material. The pattern of the security element forms the
identification characteristic 8 (see FIG. 1) and serves for example
as an optical device to catch the eye. It is advantageous to use
transparent or fully colourless materials for the protective layer
13, the carrier material 17 and the protective lacquer 19 if
provided, as the identification characteristic 8 (see FIG. 1) is
visible from both sides of the card.
As shown in FIG. 6, in a separate working operation, the
preliminary material in strip form can be processed for example to
provide a roll of stamps as indicated at 27. That is particularly
appropriate if, for technical reasons, the stamps 3 are very thin
(between about 15 .mu.m and 40 .mu.m). The patterns of the security
elements, which are regularly arranged on the preliminary material,
can be stamped out in the form of stamps 3 and the stabilization
layer 9 can be stuck by a cold adhesive onto a carrier foil 28 of
paper or plastic material. When safeguarding a document or the pass
or identity card, the stamp 3 is removed from the carrier foil 28
and stuck onto the substrate 1 (FIG. 1) and the feature 2 (FIG.
1).
The embossing dies with raised embossing structures for producing
the depressions 21 (FIG. 4a) and the relief structures 12 (FIG. 4a)
which are embossed at the floor of the recesses can be produced by
means of the numerically controlled apparatus described in EP-A-330
738, a master structure 29 of the embossing die, as illustrated in
FIG. 7a, being produced first.
The master structure 29 is fixed on a structure carrier 30. As soon
as the master structure 29 is embossed on one side with the
microscopic relief structures 12 of the pattern, it, together with
the structure carrier 30, is removed from the apparatus for coating
with a photoresist 31. The positively operating photoresist 31 is
applied in a layer thickness of between 1 and 10 .mu.m over the
entire area over the relief structures 12 of the diffraction
elements 4, 4' and over the neutral areas 5 of the exposed master
structure 29 without destroying the embossed relief structures 12.
The thickness of the layer of the photoresist 31 determines the
height of the subsequently raised embossing structures and
corresponds at least to the distance A (see FIG. 4a).
In a second pass the apparatus exposes the photoresist 31 to light
with a writing beam 32 through the structure carrier 30 of the
master structure 29, wherein the writing beam 32 is controlled by
means of the same control program over the surfaces of the
diffraction elements 4, 4' and irradiates the photoresist 31. The
process has the advantage that the photoresist 31 is irradiated
within limits 33 over the diffraction elements 4, 4' with a high
degree of register accuracy as the structure carrier 30 can be
accurately repositioned in the apparatus by means of pegs.
After development of the photoresist 31, what remains in FIG. 7b is
a master mould 34 comprising the master structure 29 which has the
photoresist 31 only on the unembossed surfaces which are between
the surfaces of the diffraction elements 4, 4'. For example, using
a galvanic process, a metal layer 35 is deposited on the surface of
the master mould 34. The metal layer 35 comprises for example
nickel and is an accurate negative of the master mould 34.
Production of the embossing die is also effected with a negatively
operating photoresist 31 if the photoresist 31 is irradiated in the
unembossed areas 5.
After separation the metal layer 35 forms the embossing die 36 with
raised embossing structures 37, as shown in FIG. 8, which can be
used for embossing the carrier material 17.
The embossing dies 36 have the advantage that, in the embossing
operation, the relief structures 12 (see FIG. 4a) are produced in
the depressions 21 (see FIG. 4a). That makes it possible to use the
above-described inexpensive processes 2 and 3 which can be used in
particular for the filigree-like patterns.
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